It is the long range goal of this application to elucidate the mechanism of action of FSH on the Sertoli cell in mammalian testis and thus provide a link between hormonal modulation of genetic information and the physiological function of the target cell. In this manner it is hoped to gain some insight into the problem of the control of regulation of the male reproductive process. The specific tasks proposed include studies to determine the role of cyclic nucleotide phosphodiesterase (PDE) in the regulation of cyclic AMP levels in the Sertoli cell. Experiments include the characterization of multiple forms of the enzymes present with respect to biochemical and kinetic properties and also how the isozymes change during development of the Sertoli cells. Results are proposed to elucidate the mechanism by which FSH inhibits PDE in the Sertoli cells of immature animals and why no such effect is demonstrable in mature animals. The major isozyme of PDE in the immature testis is calcium dependent. It is also proposed to investigate the role of calcium in the control of Sertoli cell metabolism. Studies include determination of whether FSH alters the intra- or extracellular flux of this ion and also whether hormones and/or calcium affect microtubule assembly and consequently secretion of materials from the Sertoli cell. Studies are also planned to investigate possible specific substrates that are phosphorylated upon the FSH activation of protein kinase in the Sertoli cell. Proteins to be investigated in this regard include glycogen synthase, phosphorylase kinase, PDE activator protein and tubulin. Finally, we wish to determine the role of hormones in modulating the levels and/or activity of messenger RNA in the Sertoli cell. Two major approaches will be taken. The first includes an investigation of the possibility that guanylation and/or methylation of the 5' termini of messenger RNA might be altered in response to the hormone. The second includes the isolation and partial purification of messenger RNA from the Sertoli cell and translation of the mRNA in cell free protein synthesizing systems. The specific proteins to be investigated in this regard includes PDE activator protein, protein kinase inhibitor, tubulin and androgen binding protein.